1. Field of the Invention
The present invention relates to an optical disk apparatus, and more specifically to the type of optical disk apparatus which records/reproduces data on/from an optical disk having a plurality of tracks grouped into a plurality of zones arranged in its radial direction, using a particular frequency clock for a different zone.
2. Description of the Related Art
Optical disks are formatted in advance for achieving a large storing capacity, reproduction of data accurately from a target address, and storage of data accurately into a target address. There are two known formatting modes, i.e. the CLV (constant linear velocity) mode in which the rotation of the motor is controlled in inversely proportional to the radius of the track, and the track is followed at a constant linear speed at all times, and the CAV (constant angular velocity) mode in which the rotation of the optical disk is set at constant.
As compared to the CLV mode, the CAV mode provides an easier control of the motor which rotates the optical disk; however, it has conventionally been limited to a small memory capacity. In order to increase the memory capacity of the optical disk using the CAV mode, the Z.CAV (zone constant angular velocity) mode or the M.CAV (modified constant angular velocity) mode is used as a further formatting method. In either of the Z.CAV mode or the M.CAV mode, an optical disk is divided into a plurality of zones each formed of a plurality of tracks arranged in its radial direction. Each zone has the same number of selectors per one track within that zone, and a different zone has the different number of selectors per one track. According to the Z.CAV mode, when data is stored onto an optical disk or when data is reproduced therefrom, the optical disk is rotated at a constant speed, and the storing or reproducing operation is carried out by using an optical head with reference to a particular frequency clock which is different from one zone to another. More specifically, each time the optical head accesses a track of a different zone, the reference clock frequency is renewed. Then, data is stored in the track, and the data is reproduced from the track.
On an optical disk formatted in the Z.CAV mode, a sector mark is stored in the header. That is, pre-format data, and address data is also stored therein to follow the sector mark. In order to access to a target track, the following access operation is usually carried out. The sector mark of the track currently reproduced is detected, and the address data which follows the sector mark is read. Then, the difference between the target track to be accessed and the track currently being read is calculated, and the optical head is moved over the number of tracks which corresponds to the difference.
However, such an optical disk formatted by the Z.CAV mode has a drawback, in which the normal accessing operation cannot be recovered if an error ever occurs during the access operation. More specifically, the optical head moves to a location apart from the target zone by an erroneous access operation, the sector mark cannot be detected with reference to the clock of the zone to which the target track belong, and the address data cannot be read. Consequently, the optical disk apparatus cannot carry out the following operation for correcting the erroneous access operation.
As described above, with the optical disk which employs the format by which the disk is divided into a plurality of zones each formed of a plurality of tracks arranged in the radial direction, the address cannot be read if the optical head moves to a location other than the target zone, taking a great amount of time in access operation.